The long-term objective of initiating this research program is to characterize the effect of endogenous glycosaminoglycans (GAGs) and exogenous sulfated saccharides on the function of cationic antimicrobial peptides (CAPs) in innate immunity against pathogens. In order to understand the effects of GAGs and sulfated saccharides on CAPs it is vital to first identify the individual GAGs and sulfated saccharides that bind CAPs and inhibit CAP antibacterial activity, and to characterize these interactions. The specific goal of this exploratory R21 study is to break new ground in understanding the structural requirements for endogenous GAGs and exogenous sulfated saccharides to bind CAPs and inhibit CAP antibacterial activity. In Aim 1 we will systematically identify the endogenous GAGs that bind to and inhibit antibacterial activity of individual CAPs and classes of CAPs. Susceptibility testing will be employed to quantify inhibition of CAP antibacterial activity by GAGs and GAG derivatives. Binding studies will be employed to ascertain correlations between GAG-CAP affinity and GAG inhibition of CAP activity. Completion of Aim 1 will enable future studies to dissect the role of specific CAP-GAG interactions in the infective and virulence processes of microorganisms. In Aim 2 we will determine the effect of sulfated saccharides that are in clinical use or clinical development on the antibacterial activity of individual CAPs. The central question we will answer is - Which specific types of sulfated saccharides inhibit antibacterial activity of specific CAPs in vitro, and thus have the potential to inhibit innate immune response in vivo? Completion of Aim 2 will enable future studies to determine the in vivo effects of sulfated saccharides on CAP function. Experiments in Aim 3 focus on characterizing the concentration-dependent inhibition of CAP antibacterial activity by GAGs versus GAGs protecting CAPs from proteolytic degradation. These experiments will test the hypothesis that GAGs protect CAPs from proteolytic degradation at concentrations insufficient to block CAP antibacterial activity. Relevance to public health: Molecules called antimicrobial peptides defend the body against microorganisms such as viruses and bacteria. In this study we are working to determine how activity of these antimicrobial peptides is affected by another class of molecules in the body, the glycosaminoglycans. We are also investigating if certain types of therapeutic agents inhibit antibacterial activity of the antimicrobial peptides. [unreadable] [unreadable] [unreadable]